Acoustic coupler for condenser microphones



Aug. 13, 1946. H. c. SILENT ACOUSTIC COUPLER FOR CONDENSER MICROPHONES Filed Nov. 29, 1944 5:: a m I:

.0 \\N\\\\\\ \\\\N\\\\\ \\\\\\\\\\\\\\N mm q 7 AN \N\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\% Patented Aug. 13, 1946 ACOUSTIC COUPLER FOB, CONDENSER MCROPHONES Harold 0. Silent, Los Angeles, Calif., assignor to the Government of the United States of America, as represented by the Secretary of the Navy Application November 29, 1944, Serial No. 565,757

6 Claims. 1

This invention relates to an acoustic coupler for transmitting sound waves to a condenser microphone while excluding moisture and dust particles from the microphone assembly.

It is an object of this invention to provide means for efficiently transmitting sound waves to microphones and which will prevent impairment of the functioning of the microphone due to access of dust or moisture when used under field conditions.

A further object is to provide such a device with means to control, to a limited extent, the frequency response of the device.

The single figure of the drawing shows in enlarged longitudinal section a satisfactory embodiment of my invention.

It is well known that microphones are used in military operations to pick up the sounds of gun fire and thereby to determine the distance and location of such guns and, to a certain extent, the caliber of the guns.

The most frequent equipment failure encountered with such instruments when the microphone is of the condenser type is in the condenser element, wherein the small space between the stator plate and the diaphragm is exposed to an outer chamber through a filter plug pierced with several small holes, and the outer chamber is in turn open to the atmosphere through a similar plug. These passages offer no barrier to the entrance of dust particles and moisture laden air into the condenser element as a result of temperature and barometric pressure changes.

The entrance of moisture not only reduces the necessarily high resistance of the condenser, resulting in loss of sensitivity, but causes the element to become erratic or noisy. The presence of even exceedingly small quantities of dust in the condenser chamber which usually is a space of only 0.006 inch will cause noisy and erratic operation of the instrument. The reconditioning of a microphone under field conditions is extremely difiioult to accomplish. Accordingly, the coupler constituting the present invention has been devised to protect the microphone against the entry of dust and moisture.

Referring now to the drawing, it will be noted that the coupler comprises in general a tubular assembly constituted by the major portions I and 2. Fixed to one end of the member I, as by sweating or brazing, is a flange 3 having formed thereon a shoulder 4. Secured to the flange 3 is an element having a tubular portion of the same radial dimensions as members I and 2 and also having a radially extending flange 6 that serves to clamp the ring I and thin rubber diaphragm 8 against the flange 3. The diaphragm 8 is of such thickness and elasticity as to transmit sound without substantial attenuation of the sound energy.

Fixed on one end of member 2 is the element 9 which has a. cylindrical portion I0 that fits snugly upon the shoulder 4 and is also provided with a shoulder H to bind the gasket l2 tightly against flange 6. Cooperating with the member 0 to form an enclosed annular chamber is the sleeve !0 that covers the joint between members 2 and 5. The chamber so formed is filled with a hygroscopic, or desiccant granular material I 3 which is retained by fibrous or filamentary material [4 and a fine Wire screen It? from passing into the breathor ducts l6 and [1. An opening 26, stopped by a closure 21, is provided for observing when the desiccant l3 should be replenished or renewed.

Secured to the member 9 at one end and to the end element l8 at the other, surrounding member 2 and spaced therefrom, is a highly flexible rubber bellows I9. This bellows is held in air tight relation to the members 9 and I8 by tightly drawn threads 20 disposed over the bellows I!) in grooves. Bellows I9 is protected externally by a sleeve 2| which may be of any suitable material' such as one of the well known synthetic plastics provided with an opening through which atmospheric pressure may act upon bellows l3. The construction just described confines a body of air within the tubular assembly back of the diaphragm B and inside the bellows IS. The pres sure on the opposite sides of diaphragm 8 is thus equalized by movement of air between the space enclosed by bellows l9 and member 2, and the space in the member 2 by way of the ducts l5 and I! and through the desiccant material I3 and thus any moisture in the air so confined is removed as it passes through the desiccant material l3 in response to variations of atmospheric pressure.

The end element I8 is provided with external threads 22 for connecting the coupler to the microphone housing in place of the filter plugs above mentioned. The passages 23 through the end element 18 permit transmission of sound waves to the microphone mechanism. A remov- I able screw 24 is disposed in the end element l8 and may be taken out when it is desired that the upper limit of the frequency response of the device should be raised. For example, with the screw 24 in place the upper limit of response may be cycles per second but when it is removed that upper limit will be cycles per second.

The end of the assembly remote from the microphone is preferably provided with a wire screen to prevent entry of any large particles of dirt or other matter that might damage, or interfere with the sound response of, diaphragm ii.

I claim:

1. An acoustic coupler for a condenser microphone having a single restricted opening for access of sound Waves thereto, comprising a first tub lar part having an internal shoulder adjacen one end, a second tubular part having one of its ends secured in the said one end of the first part, a thin rubber diaphragm clamped in position between said shoulder and the said one end of the second part to close the opening through the parts against moisture and dirt, means defining a closed annular chamber around a portion of said first part, a body of granular disiccant in said chamber, a flexible member surrounding the major portion of said first part secured at its ends to said first part in air-tight relation and spaced therefrom between its ends, there being ducts connecting said annular chamber to the space within said member and other ducts connecting said chamber to the space within said first part, matter filamentary mate-- rial disposed to exclude the disiccant from said ducts, and an end member fixed to and substantially closing the other end of the first part, said member being provided with elements to secure the coupler to the microphone to conduct sound to said opening in the microphone and with passages for the transmission of the sound, and a removable closure in one of said passages which, when the closure is removed, renders the device effectively responsive to higher sound frequencies than when the closure is in the passage.

2. An acoustic coupler for a condenser microphone having a single restricted opening for access of sound waves thereto, comprising a, first tubular part having internal shoulder adjacent one end, a second tubular part having one of its ends secured in the said one end of the first part, a thin rubber diaphragm clamped in position. between said shoulder and the said one end of the second part to close the opening through the parts against moisture and dirt, means defining closed annular chamber around a portion of said first part, a body of granular desicant in said chamber, a flexible member surrounding the major portion of said first part seured at its ends to said first part in air-tight reation and spaced therefrom between its ends, there being ducts connecting said annular chamber to the space within said member and other ducts connecting said chamber to the space within said first part, matter filamentary material disposed to exclude the desiccant from said ducts, and an end member fixed to and substantially closing the other end of the first part, said memher being provided with elements to secure the coupler to the microphone to conduct sound to said opening in the microphone and with passages for the transmission of the sound.

3. An acoustic coupler for a condenser microphone having a single restricted opening for access of sound waves thereto, comprising a first tubular part having an internal shoulder adjacent one end, a second tubular part having one of its ends secured in the said one end of the first part, a thin rubber diaphragm clamped in position between said shoulder and the said one end of the second part to close the opening through the parts against moisture and dirt, breather means including a fiexible member responsive to changes in air pressure disposed in air-tight relation around the first part and spaced therefrom to enclose a body of air, a confined body of desiccant material, and ducts to permit passage of air between said body of air and the interior of the first part through the desiccant material.

4. An acoustic coupler for a condenser microphone having a single restricted opening for access of sound. waves thereto, comprising a first tubular part having an internal shoulder adjacent one end, a second tubular part having one of its ends secured in the said one end of the first part, a thin rubber diaphragm clamped in position between said shoulder and the said one end of the second part to close the opening through the parts against moisture and dirt, means to equalize air pressure on opposite sides of the diaphragm including a member cooperating with the first part to define an enclosed space having a volume that is variable with changes in air pressure, passages to permit movement of air between said space and the interior of the first part, and an enclosed body of hygroscopic material disposed in the path of air moving between the interior of the first part and said space.

5. An acoustic coupler for a condenser microphone having a single restricted opening for access of sound waves thereto, comprising a tubular assembly, a thin rubber diaphragm across the interior thereof intermediate its ends, a member fixed to one end of the assembly to attach the assembly to the microphone in operative relation to said opening, said member having passages for transmission of sound waves to the microphone, means associated with a said passage to vary the sound frequency response, means to enclose a volume of air Variable in response to changes in the ambient air pressure connected to the space between the diaphragm and the said member, and material to remove moisture from air passing between said space and said volume of air.

6. An acoustic coupler for a condenser microphone having a single restricted opening for access of sound waves thereto, comprising a tubular assembly, a moisture and dust excluding diaphragm across the interior thereof intermediate its ends, said diaphragm transmitting sound waves without substantial attenuation of the sound, a member fixed to one end of the assembly to attach the assembly to the microphone in operative relation to said opening, said member having passages for the transmission of sound waves to the microphone, means associated with a said passage to vary the sound frequency response, means to enclose a volume of air in response to changes in the ambient air pressure connected to the space between the diaphragm and the said member, and material to remove moisture from air passing between said space and the said volume of air.

HAROLD C. SILENT. 

